The vibration of articles of furniture for inducing relaxation in the user has been accomplished in the prior art using a variety of mechanisms. Because of the ready availability of high power, 60-cycle current, however, the bulk of these systems have used either a direct 60-cycle transducer to induce vibration or a motor with an eccentric weight operating from the 60-cycle current. In some instances where a motor with an eccentric weight is used, the speed of the motor is variable, for example, using a solid state control or a rheostat. Such devices, however, necessarily control the amplitude and frequency of vibration simultaneously, and it is impossible, without altering the eccentricity of the weight (a difficult operation) to alter the frequency and vibration independently.
In systems where two eccentric weight motors are used on a single piece of furniture, it has been found that interference waves can be produced in the furniture, which waves result in a pleasant sensation for the user. These systems, however, as mentioned above, can produce such interference waves only at predetermined amplitudes depending completely upon the frequency selected for motor operation.
Thus, in the prior art, vibration transducers have typically been limited to operation from the available 60-cycle current and have not been utilized to independently vary the frequency and amplitude of the vibration. Motors used in the prior art are limited in the variation of waves which may be induced and, furthermore, are subject to substantial wear generated by the eccentric weight.